The present invention relates to speed regulating devices for rotary machines or the like.
In conventional speed regulating devices, the output from a tachometer such as a generator coupled to the driving shaft of a motor is converted by a waveshaping circuit into trigger pulses which, in turn, are converted by a waveform converting circuit into rectangular waveform signals with a predetermined time interval T.sub.S and a pulse repetition rate which changes in response to the frequency of the output from the generator. The rectangular waveform output signals are smoothed by a smoothing circuit, and in response to the output from the smoothing circuit, a driving circuit controls the motor so as to rotate at a predetermined rate. The conventional speed regulating devices have, however, an inherent limitation in that the control of the rotational speed of a rotary machine or the like with a high degree of accuracy cannot be attained, because the output voltage from the driving circuit changes in response to variations in supply voltage.
To overcome this problem, a system has been devised and demonstrated in which a voltage regulator is connected to the output of the waveshaping circuit, so that the stable voltage may be applied to the waveform converting circuit in the next stage. However, when the supply voltage changes over a wide range, the output from the driving circuit also changes slightly, and the output voltage from the voltage regulator also changes. Therefore, it is difficult to control the rotational speed of the rotary machines with a high degree of accuracy. In conventional speed regulating devices, the gain of the driving circuit must be considerably increased if the control with a high degree of accuracy is desired.